This invention relates to the manufacture of footwear. More particularly, this invention relates to methods of lasting shoe uppers to a footform or last, and to articles of footwear produced thereby.
Various methods of lasting such as cord, wire, string, slip and welt lasting of shoe uppers are well known in the manufacturing of footwear. In string lasting for example, a string is loosely attached to the marginal edge or lasting margin of a shoe upper for example, by a loose overstitch such that, when pulled, the string can slip within the confines of the overstitch. The shoe upper having the string attached thereto is then placed loosely over a footform or a last such that the shoe upper lasting margin is adjacent the last contoured or feathered edge which adjoins the last sides with the last bottom or sole. The lasting string is then drawn on pulled tightly to thereby gather, pull and draw a portion of the shoe upper lasting margin over the last feather edge to closely conform the shoe upper to the contour of the last, and the lasted-over margin to the contour of the last feathered edge and at least the outer margin of the of the last sole. This pulling-over operation also helps prevent wrinkles from appearing in the shoe upper above the sole. The shoe upper lasted-over margin is held in the lasted-over position by somehow attaching or fastening it to the last sole or to an insole placed thereover, the example, by cementing, tacking, stapling, stitching or molding operations, or by holding or tying the string, for example, by wrapping it around pins fixed to the last sole or to a shank thereon, until the attaching or other fastening operation is complete. The shoe upper is then ready for outsoling by cementing, nailing, stapling, sewing or for example, molding an outsole to its lasted-over margin to complete fabrication of the article of footwear.
Heretofore, the pulling of the lasting string to pull, draw or gather a portion of the shoe upper lasting margin tightly over the last feather edge, has been effected manually or mechanically. Either is disadvantageous for several reasons. A manual operation requires skill and great strength. It is hazardous because it often cuts, bruises, and causes blisters and callouses on the operator's hands. Gloves or protective materials such as wrappings are usually required. These reduce dexterity and lessen effectiveness of the operation. It also results in a high turnover of personnel which in turn requires training and apprenticeship periods for new people during which there are hourly and daily variations in pulling strength, qualitative and quantitative variations in workmanship, and high spoilage. Another disadvantage of a manual operation is that heavy gauge leathers must be extensively and often repeatedly wetted to render then stretchable and lastable by human labor.
To overcome or avoid the aforementioned and other problems, complicated power-driven machinery is commonly employed to do the pulling, by, for example, power-driven arms having grasping means for grasping and pulling the lasting strings, or by pins or posts which are rotatably driven to exert a pulling force on lasting strings wrapped therearound. Mechanical means are also employed for wiping, for example, the toe portions of a shoe upper over the last to smooth out folds which sometimes occur due to the noosing and bunching of the material as it is gathered and drawn over the feather edge and forced to conform to various concave and convex shapes of the folds or the last. But, employing mechanical machinery for lasting operations is disadvantageous because it is very expensive. It requires high capital investment and frequent complicated maintenance, and it utilizes much energy. Another disadvantage of currently employed string pulling and holding methods is that the rotatably driven pins or posts on the last soles or shanks about which the lasting strings are wrapped, often are damaged or break and require repair, replacement or maintenance of the last.
Regardless of whether pulling of the lasting string is effected manually or mechanically, the lasting operation itself has heretofore been a bottleneck which has precluded fully automated, high-speed production of footwear. The pulling operation has heretofore not been considered to be fully automatable.
The method of this invention overcomes all of the aforementioned and other disadvantages by providing a method of lasting a shoe upper to a last, which eliminates the need for human or power-driven mechanical pulling forces and eliminates all of the problems associated therewith. The method is safe and is capable of providing consistent pulls of equal force which in turn provide monetary savings through consistent high quality lastings with little or no spoilage. Compared to power-driven mechanical means, the method is less costly. Capital investments are less and maintenance and energy requirements are less. Full automation of the drawing operation is feasible and allows for more uniform, higher quality, higher throughput production at lower cost. Also, the need for lasting pins or posts and problems associated therewith can be eliminated.